Glass fibers are typically formed by attenuating filaments through bushing tips located at the bottom of a heated bushing containing molten glass. The fibers are then passed across an application surface of an applicator where they are coated with a binder and/or size. The filaments are then passed into a gathering means, such as a gathering shoe, which is typically a grooved wheel or cylinder formed of a material such as graphite, with the glass filaments being combined into a unified strand within the groove of the gathering shoe. In some operations, the binder and/or size is applied to the filaments at the gathering means, with these two steps both being performed by a single apparatus, such as a pad applicator.
After the filaments are gathered into a unified strand, the strand is then traversed over a rotating spiral or a reciprocating cam and is collected on a rotating drum or collet as a forming package. In other operations, the strand formed may be chopped into a plurality of particulate strands or passed between belts, wheels or a combination of belts and wheels and attenuated onto a surface as mat or collected in a container. The attenuative forces necessary to form the filaments and strand are produced by either the rotating collet, the chopping apparatus or the attenuator, depending upon the operation being performed.
It is important in the production of glass fibers that a sufficient amount of binder and/or size be applied to the filaments before the filaments come into direct contact with one another. Should the glass filaments come into direct contact with each other without a binder or size present on them the filaments can readily break due to abrasion. Broken filaments can cause a weakened strand to be formed, resulting in fuzz in the strands formed and, if enough filaments are broken, lead to a completely broken strand. In order to reduce or eliminate these occurrences, it is common to apply an excess of binder and/or size to the filaments as they are formed to ensure that every filament is sufficiently coated with a high degree of certainty.
The overcoating of the glass filaments with binder and/or size causes its own problems. During attenuation, this liquid binder and/or size is sometimes thrown from the surfaces of the filaments, which are traveling at a high linear rate of speed, typically on the order of 1,000 to 20,000 feet per minute (324.8 to 6496 meters per minute). This causes housekeeping problems in the fiber forming area.
Another problem associated with the preparation of forming packages or containerized packages of glass strand with excess binder and/or size thereon, is the problem of binder migration. After the forming package or containerized package is produced, it is subjected to a baking operation to remove moisture from the strand. During this process, excess binder and/or size in the forming package or containerized package tends to migrate to the innermost and outermost regions of the package, causing an excess of binder and/or size solids on the strands at the inside and outside of the package. This, of course, results in an inconsistant strand and is thus highly undesirable.
It is desirable, therefore, to produce glass strands which do not have an excess binder and/or size thereon when they are collected but which still have been coated to an extent such that they have sufficient binder and/or size thereon with a high degree of certainty to assure complete coverage of the filaments.
A further problem associated with excess binder and/or size on glass strand is that the excess binder and/or size which is either thrown off in liquid form from the strand as it is being collected or baked from the strand package and migrated to the surfaces of the package is wasted material. This adds significantly to the cost of producing the strand and thus reduces the profitability of the product.
It is also desirable, therefore, to recover any excess binder and/or size which has been applied to the filaments so that this material can be recycled through the application system.
In U.S. Pat. No. 3,029,161 an apparatus is illustrated for recovering excess binder from a pad applicator. This apparatus recovers only the excess binder and/or size dripping from the applicator pad surface. There is no teaching in this patent of removing excess binder from the strand surfaces after the binder and/or size is applied to the filaments and recovering this material.
U.S. Pat. No. 3,977,854 illustrates an apparatus which removes excess binder and/or size from the strand after the filaments have been coated. This apparatus diverts a portion of the air normally flowing downwardly with the filaments across the strand surface. Thus, this patent requires that the normal airflow associated with the filament formation be diverted from its normal downward path. Such diversion in airflow patterns can affect the operation of the forming position, since successful glass fiber formation is highly dependent upon control of the bushing environment and the airflows associated therewith. The apparatus of this patent also requires a deflector shield for accomplishing this result. It is thus an object of the present invention to recover excess binder and/or size from glass strand without the need of diverting air from its normal downward flow pattern with the filaments in a fiber forming operation and without the necessity of auxiliary apparatus for diverting air flowing downwardly with the filaments and strand.